Search

The Metabolic Scaling Theory (MST), hypothesizes limitations of resource-transport networks in organisms and predicts their optimization into fractal-like structures. As a result, the relationship between population growth rate and body size should follow a cross-species universal quarter-power scaling. However, the universality of metabolic scaling has been challenged, particularly across transitions from bacteria to protists to multicellulars. The population growth rate of unicellulars should be constrained by external diffusion, ruling nutrient uptake, and internal diffusion, operating nutrient distribution. Both constraints intensify with increasing size possibly leading to shifting in the scaling exponent. We focused on unicellular algae Micrasterias. Large size and fractal-like morphology make this species a transitional group between unicellular and multicellular organisms in the evolution of allometry. We tested MST predictions using measurements of growth rate, size, and morphology-related traits. We showed that growth scaling of Micrasterias follows MST predictions, reflecting constraints by internal diffusion transport. Cell fractality and density decrease led to a proportional increase in surface area with body mass relaxing external constraints. Complex allometric optimization enables to maintain quarter-power scaling of population growth rate even with a large unicellular plan. Overall, our findings support fractality as a key factor in the evolution of biological scaling. [ABSTRACT FROM AUTHOR]

We studied the biodiversity of Asterochloris photobionts found in Bolivian lichens to better understand their global spatial distribution and adaptation strategies in the context of a worldwide phylogeny of the genus. Based on nuclear ITS rDNA, the chloroplast rbcL gene and the actin type I gene we reconstructed a phylogenetic tree that recovered nine new Asterochloris lineages, while 32 Bolivian photobiont samples were assigned to 12 previously recognized Asterochloris lineages. We also show that some previously discovered Asterochloris photobiont species and lineages may occur in a broader spectrum of climatic conditions, and mycobiont species and photobionts may show different preferences along an altitude gradient. To reveal general patterns of of mycobiont specificity towards the photobiont in Asterochloris, we tested the influence of climate, altitude, geographical distance and effects of symbiotic partner (mycobiont) at the species level of three genera of lichen forming fungi: Stereocaulon, Cladonia and Lepraria. Further, we compared the specificity of mycobionts towards Asterochloris photobionts in cosmopolitan, Neotropical, and Pantropical lichen forming fungi. Interestingly, cosmopolitan species showed the lowest specificity to their photobionts, but also the lowest haplotype diversity. Neotropical and Paleotropical mycobionts, however, were more specific. [ABSTRACT FROM AUTHOR]

Vegetative propagules play various important roles in lichen biology. We cultured soredia of Cladonia lichens in vitro and obtained three noteworthy results. Firstly, soredia are a beneficial source for the isolation of lichen symbionts. The mycobiont was obtained from 66% and the photobiont from 67% of the cultured soredia that were not contaminated. Secondly, the development of soredia followed a previously recognized pattern, arachnoid stage – soredium field – primordium, but a thalline structure was not achieved. We suggest that thallus formation in vitro is a question of favourable environmental factors, not partners compatibility. Finally, we discovered that fungi, other than the mycobiont, as well as airborne contaminants are dispersed together with lichen soredia. This is the first-ever report of such a phenomenon. The possible ecological consequences are discussed. Cystobasidiomycete yeasts were found among these fungi. We isolated representatives of three different lineages from a single thallus suggesting a low specificity for this association. [ABSTRACT FROM AUTHOR]

Dispersal limitation, niche-based processes as well as historical legacies shape microbial biodiversity, but their respective influences remain unknown for many groups of microbes. We analysed metacommunity structure and functional trait variation in 148 communities of desmids, freshwater green algae, distributed throughout Europe. We delineated biogeographic modules for both taxa and sites using bipartite network analysis given that the taxa of a module co-occurred more often than expected by chance in sites of the same module. The network analysis distinguished two main acidic and neutral habitats, reflecting environmental filtering, and within each habitat separated species pools with distinct geographic locations, representing a plausible influence of historical biogeography. The geographic differentiation was consistent with a hypothesis of glacial refugia on Atlantic coast. Distance decay in community composition in addition to environmental influence further suggested a role of dispersal limitation. Next, we quantified the variation in cell volume and surface-to-volume of taxa within and among communities, to examine morphological and physiological adaptations of desmids in varying environments. Communities from continental climate contained larger desmids. Conversely, we found a functional convergence of smaller, fast-growing, desmids in oceanic regions. Overall, our findings suggest that niche-based processes, dispersal limitation, and historical legacy together drive the distribution and structure of desmid communities. Combining trait- and network-based analyses can resolve long-lasting questions in microbial ecology and biogeography, and could be successfully used in macrobial ecology too. [ABSTRACT FROM AUTHOR]

Natural surface coatings (biofilms) were collected on glass slides in the shallow, arsenic-rich stream and were used to compare biofilm trace element adsorption properties. Biofilm element retention and affinities were element specific indicating different processes control their sequestration. Distribution coefficients ( K values), calculated as the ratio between biofilm and dissolved trace element concentrations, revealed solid phase enrichment that, depending on the trace element, extended from 10 to 10. Elements were specifically scavenged by the organic constituents of the biofilm itself (Fe, Pb, Zn, Cr) and associated biominerals of poorly ordered Mn oxide (Cd, As, Mo, Sb). The results provide an evidence for the significant role that microbial activity can play in trace element geochemistry in freshwater environment. [ABSTRACT FROM AUTHOR]

Freshwater filamentous green algae with branched thalli are almost unknown from the Antarctic region. They have rarely been recorded from maritime Antarctica and from sub-Antarctic Islands with rich phanerogamic vegetation. In the genus Hazenia, only one unidentified species was reported from several subaerial sites on Signy Island in 1979. However, unique populations of this genus were recently found in the stony littoral zone of two stable shallow lakes in the northern deglaciated region of James Ross Island (NE Antarctic Peninsula). These populations have a specialized ecology; they participate in the microvegetation on the flattened surfaces of stones in the littoral zones of lakes. The dominant green filamentous and richly branched alga from these communities was transferred to monospecific culture and studied in detail. Molecular sequence data (18S ribosomal DNA and the internal transcribed spacer) indicate that it belongs to the genus Hazenia (Bold in Am J Bot 45:737-743, ). Based on distinct molecular, morphological, and ecological characters, this alga was described as a new species ( Hazenia broadyi spec. nova). A review of the genus Hazenia, based on molecular phylogenetic analyses of available strains, was also performed. [ABSTRACT FROM AUTHOR]

Morphological species of freshwater microalgae often have broad geographic distribution. However, traditional species concepts have been challenged by the results of molecular phylogenetic analyses that mostly indicate higher diversity than was previously recognized by purely morphological approaches. A degree of phenotypic differentiation or different geographic distribution of species defined by molecular data remains largely unknown. In this study, we analyzed a pair of well-known and widely distributed desmid species ( Micrasterias fimbriata and M. rotata) and tested for their phylogenetic and morphological homogeneity as well as their geographic distribution. Geometric morphometric and morphological attributes of cells were used in combination with genetic analysis of the trnG sequences of 30 strains isolated from a variety of European locations and obtained from culture collections. Micrasterias rotata proved to be phylogenetically homogenous across Europe while M. fimbriata turned out to be composed of two firmly delimited lineages, differing by molecular as well as by morphometric and morphological data. Published records of traditional M. fimbriata were also included in the classification discrimination analysis and were placed into the newly identified lineages upon comparison to the morphometric data collected from living material. Largely disparate geographic patterns were revealed within traditional M. fimbriata. One phylogenetic lineage is frequent in central and eastern Europe, but occurs also in the British Isles. A second lineage has been recorded in North America and in Western Europe, where its distribution is possibly limited to the west of the Rhine River. Interestingly, the morphometric analyses of the published records illustrated that the geographic differences have remained largely unchanged since the 1850s indicating a previously unknown distributional stability among microalgal species groups such as the desmids. [ABSTRACT FROM AUTHOR]

Although epipelic diatoms play a key role in primary production of many ecosystems, many aspects of their biodiversity, ecology and geographical distribution are poorly understood. The present study is based on sampling of 45 man-made fishponds in the Czech Republic covering an environmental gradient from oligo/dystrophic highland ponds within protected areas to the eutrophic/hypertrophic lowland ponds used for intensive fish production. Diatom distribution patterns assessed using biomass and species composition variables were assessed along environmental and geographical gradients. In total, 185 epipelic diatom taxa were found in the investigated samples. The differences in species composition between sites were correlated with environmental parameters, but not with the geographic distance of the localities. This pattern might suggest that niche-based control, rather than the effect of dispersal limitation, is the main driving force in the species composition of epipelic diatoms in fishponds. The alpha-diversity of sites correlated with altitude, nitrogen and chlorophyll a concentrations but did not correlate with the area of the ponds. The significant relationships between local abundance of species and their regional occupancy were very similar to previous studies of diatoms in boreal streams. In addition, these data concur with patterns known for multicellular organisms suggesting that in this respect diatoms may not differ from groups of organisms with larger body sizes. [ABSTRACT FROM AUTHOR]